Collaborative Research: Novel Modular High-density High-efficiency medium voltage power converter

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

Novel Modular High-density High-efficiency Medium-voltage Power Converter High power solid-state power converter is a critical component in many applications, such as accessing renewables energy and energy storages from grid, e.g. solar, wind, and batteries and driving high power motors. Traditionally, most of such power converter are rated below 1 kilovolt or within lower voltage class for its simplicity. Recently, for further system cost reduction and efficiency improvement, industry is moving toward medium-voltage solutions, which can directly access the medium voltage grid, to save bulky transformer, cables and cost of the converter. To achieve such goal, it is desirable to develop a medium voltage high-power solid-state power converter, which is high-efficient, high power density/low volume and with ac output waveform close to an ideal sinusoidal waveform. To address such desire, the principle investigators proposed a novel modular high density medium-voltage power converter topology, namely three-level hybrid modular multilevel converter, which combines branches with cascaded modular cells and traditional three-level structure. The proposed concept leads to various topology variations for medium voltage application. In particular, the rectifier variation with diode as the three level structure can provide a significant cost and total system size saving and efficiency improvement compared to classic modular multilevel converter solution. Compared with the state of art solution, this proposed solution can reduce the converter volume/weight by up to 50% and the improve the converter efficiency by up to 30% while achieve the same voltage and current rating. In addition, thanks to the modular design, the proposed solution can also achieve high-fidelity ac output and can be scaled up to higher voltage rating for future applications without intensive engineering design rework. The low voltage and medium voltage silicon carbide devices can be used in the proposed family of topologies to leverage its switching-loss savings to synthesize high-fidelity ac output. Such modular design also means built-in system redundancy which can substantially improve system reliability. Thus, the intellectual merits of the proposed solution will make a strong impact on a broad range of medium voltage power conversion applications, like renewable energy grid-integration, subsea and offshore dc power delivery, naval medium voltage direct current power system, industrial variable speed drives, and transportation high-speed electric propulsion system. There are many fundamental control challenges and operation analysis for this topology and its variations. Through the proposed program, the detailed topology and operation analysis of the family of proposal converter topology will be performed for both unity power factor and non-unity power factor conditions. The phase-arm and phase energy balancing strategies will be explored and verified in simulation. And its benefits will be analyzed through detailed engineering design for down-selected example systems, including fault handling capability. In the end, scaled prototypes will be developed to demonstrate its innovation and benefit to industry. The unique industry consortium and Navy collaboration provided by the universities will foster a collaborative relationship among industry members, Navy R&D community, and academic researchers, which will consequently make a strong impact through this NSF research program. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.